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- $ {l^2} = {h^2} + {R^2}$.
- $ \\\frac{1}{{{l^2}}} = \\\frac{1}{{{h^2}}} + \\\frac{1}{{{R^2}}}$.
- $ {l^2} = hR$.
- $ {R^2} = {h^2} + {l^2}$.